Pneumatic Pressure Output Control by Drive Valve Duty Cycle Calibration

ABSTRACT

In various embodiments, a surgical console may include a pneumatic valve to drive a pneumatic tool coupled to the surgical console. The console may further include a controller operable to control and adjust the valve open/close cycle times according to a valve duty cycle. The valve may switch between ports (valve open time for a first port and valve close time for a second port) such that a total valve time may approximately equal the valve open time plus the valve close time. The valve duty cycle may indicate a percentage of the total valve time for the controller to signal the valve to open and may include an adjustment that corresponds to a signal timing of the open and/or closed valve positions that will result in open and closed operating pressures above a predetermined threshold.

PRIORITY CLAIM

This application claims the benefit of priority of U.S. ProvisionalPatent Application Ser. No. 61/238,431 titled “Pneumatic Pressure OutputControl By Drive Valve Duty Cycle Calibration”, filed on Aug. 31, 2009,whose inventors are Jiansheng Zhou, Kurt Leukanech, and Dan Teodorescu,which is hereby incorporated by reference in its entirety as thoughfully and completely set forth herein.

FIELD OF THE INVENTION

The present invention generally pertains to calibration. Moreparticularly, but not by way of limitation, the present inventionpertains to calibration for a pneumatic surgical system.

DESCRIPTION OF THE RELATED ART

Vitreo-retinal procedures include a variety of surgical proceduresperformed to restore, preserve, and enhance vision. Vitreo-retinalprocedures are appropriate to treat many serious conditions of the backof the eye. Vitreo-retinal procedures treat conditions such asage-related macular degeneration (AMD), diabetic retinopathy anddiabetic vitreous hemorrhage, macular hole, retinal detachment,epiretinal membrane, CMV retinitis, and many other ophthalmicconditions.

The vitreous is a normally clear, gel-like substance that fills thecenter of the eye. It makes up approximately ⅔ of the eye's volume,giving it form and shape before birth. Certain problems affecting theback of the eye may require a vitrectomy, or surgical removal of thevitreous.

A vitrectomy may be performed to clear blood and debris from the eye, toremove scar tissue, or to alleviate traction on the retina. Blood,inflammatory cells, debris, and scar tissue obscure light as it passesthrough the eye to the retina, resulting in blurred vision. The vitreousis also removed if it is pulling or tugging the retina from its normalposition. Some of the most common eye conditions that require vitrectomyinclude complications from diabetic retinopathy such as retinaldetachment or bleeding, macular hole, retinal detachment, pre-retinalmembrane fibrosis, bleeding inside the eye (vitreous hemorrhage), injuryor infection, and certain problems related to previous eye surgery.Vitrectomies may be performed in the anterior or posterior portions ofthe eye. While an anterior vitrectomy may be a planned procedureperformed in such settings as traumatic cataract removal or secondaryIOL (intraocular lens) placement, an anterior vitrectomy is most oftenan unplanned addition to a cataract surgery when vitreous isinadvertently prolapsing into the anterior segment after a rupture ofthe posterior capsule.

The retinal surgeon performs a vitrectomy with a microscope and speciallenses designed to provide a clear image of the back of the eye. Severaltiny incisions just a few millimeters in length are made on the sclera.The retinal surgeon inserts microsurgical instruments through theincisions such as a fiber optic light source to illuminate inside theeye, an infusion line to maintain the eye's shape during surgery, andinstruments to cut and remove the vitreous.

In a vitrectomy, the surgeon creates three tiny incisions in the eye forthree separate instruments. These incisions are placed in the pars planaof the eye, which is located just behind the iris but in front of theretina. The instruments which pass through these incisions include alight pipe, an infusion port, and the vitrectomy cutting device. Thelight pipe is the equivalent of a microscopic high-intensity flashlightfor use within the eye. The infusion port is required to replace fluidin the eye and maintain proper pressure within the eye. The vitrector,or cutting device, works like a tiny guillotine, with an oscillatingmicroscopic cutter to remove the vitreous gel in a controlled fashion.This prevents significant traction on the retina during the removal ofthe vitreous humor.

The surgical machine used to perform a vitrectomy and other surgeries onthe anterior and/or posterior of the eye is very complex. Typically,such an ophthalmic surgical machine includes a main console to which thenumerous different tools are attached. The main console provides powerto and controls the operation of the attached tools. The main consolemay also be used for performing other ophthalmic procedures such asphacoemulsification.

The attached tools typically include probes, scissors, forceps,illuminators, vitrectors, and infusion lines. Each of these tools istypically attached to the main surgical console. A computer in the mainsurgical console monitors and controls the operation of these tools.These tools also get their power from the main surgical console. Some ofthese tools are electrically powered while others are pneumaticallypowered.

In order to provide pneumatic power to the various tools, the mainsurgical console has a pneumatic or air distribution module. Thispneumatic module conditions and supplies compressed air or gas to powerthe tools. Typically, the pneumatic module is connected to a cylinderthat contains compressed gas. The pneumatic module may provide theproper gas pressure to operate the attached tools properly.

SUMMARY OF THE INVENTION

In various embodiments, a surgical console may include a pneumatic valve(e.g., a four way solenoid valve) with at least two ports operable toalternately provide pressurized gas to drive a pneumatic tool (such as avitrectomy probe) coupled to the surgical console. The surgical consolemay further include a controller operable to control and adjust thevalve open/close times according to a valve duty cycle. The valve mayswitch between ports (valve open time for a first port and valve closetime for a second port) such that a total valve time may approximatelyequal the valve open time plus the valve close time. The valve dutycycle may indicate a percentage (e.g., 50%) of the total valve time forthe controller to signal the valve to open.

Because different valve open/close timings can lead to a loss inoperating pressure, an adjustment may be made to the valve duty cycle sothat signal timing for the open and/or closed valve positions willresult in open and closed operating pressures above a predeterminedthreshold. For example, the adjusted valve duty cycle may beapproximately equal to a previous valve duty cycle+(((abs(openpressure)−abs(closed pressure))/2)*(valve duty cycle delta/differentialpressure change delta)) where the previous valve duty cycle is the valveduty cycle during testing, open pressure and closed pressure aredifferential pressures for the ports at respective open and closed timesduring one cycle of the valve, and the valve duty cycledelta/differential pressure change delta is a ratio of valve duty cyclechange to resulting differential pressure change (for example, in thevalve open pressure). For calculating the new valve duty cycle, the openpressure and closed pressure for the port may be taken during a lowestperformance point for the pneumatic system (e.g., when the absolutepressure difference between the open pressure and closed pressure is thelowest such that (abs(open pressure)+abs(closed pressure)) is at aminimum for the measured pressure data). Once determined, the valve dutycycle may be stored on a memory accessible by the controller for futureuse.

In some embodiments, a valve duty cycle may be input into the systemthrough a series of DIP switch settings. For example, the surgicalconsole may include DIP switches and resistors coupled together suchthat the DIP switches are configurable to combine one or more of theresistors in a resistor network. The DIP switches may be set such thatupon applying an input voltage to the resistor network, an outputvoltage of the resistor network is indicative of a valve duty cycle. Insome embodiments, the surgical console may include an analog to digitalconverter operable to convert the output voltage to a digital value thatsoftware executing on the surgical console can use to determine a valveduty cycle (e.g., through the use of a look-up table that associates thedigital value with an associated valve duty cycle).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference ismade to the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 illustrates a surgical console, according to an embodiment;

FIG. 2 illustrates a diagram of a pneumatic system, according to anembodiment;

FIG. 3 illustrates a controller for the pneumatic valves, according toan embodiment;

FIG. 4 illustrates a diagram of an embodiment of a pneumatic tool;

FIGS. 5 a-6 illustrate various embodiments of a DIP switch and resistornetwork;

FIG. 7 illustrates a flowchart of a method for calibrating a pneumaticssystem, according to an embodiment;

FIGS. 8 a-8 b illustrate pressure data for a pneumatic valve, accordingto an embodiment; and

FIG. 9 illustrates a calibration table, according to an embodiment.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention as claimed.

DETAILED DESCRIPTION OF THE EMBODIMENTS

U.S. Patent Application Publication entitled “Pneumatic System for aVitrector,” Publication No. 20080149197, Ser. No. 11/614,678, by DenisTurner, Robert Palino, Argelio Olivera, and Mark Hopkins filed Dec. 21,2006 is hereby incorporated by reference in its entirety as though fullyand completely set forth herein.

FIG. 1 illustrates an embodiment of a surgical console 101 for apneumatically powered ophthalmic surgical machine. The surgical console101 may operate to assist a surgeon in performing various ophthalmicsurgical procedures, such as phacoemulsification and vitrectomy. Thesurgical console 101 may include an internal monitor system, one or morecontrollers (e.g., proportional controllers), and tools (which mayinclude phacoemulsification tools and/or pneumatic tools 103). Thepneumatic tools 103 may include, for example, scissors, vitrectors,forceps, and injection or extraction modules. Other tools 103 may alsobe used. A compressed gas, such as nitrogen, may provide the power forpneumatic tools 103. The compressed gas may pass through the gaspressure monitor system, through one or more manifolds to the one ormore proportional controllers, and through additional manifolds and/ortubing to tools 103.

FIG. 2 is a schematic of a pneumatic system for a pneumatically poweredvitrectomy machine, according to an embodiment. In FIG. 2, the pneumaticsystem may include pump vent valve 205, output valve 210, mufflers 225,230, 251, 253, manifold 235, and output ports A and B for respectivepneumatic channels to power a pneumatic tool 103 (e.g., see FIG. 4).

In some embodiments, pump vent valve 205 may be a four-way valve. Valve205 may include a solenoid that operates to move the valve to one of atleast two positions. In one position, pressurized gas may pass throughpump vent valve 205 and out of muffler 230. In another position, pumpvent valve 205 may allow pressurized gas to pass through pump vent valve205 to provide power to the tool 103. Pump vent valve 205 may becontrolled by a controller (e.g., controller 300 as seen in FIG. 3).

In some embodiments, output valve 210 may be a four-way valve. Valve 210may include a solenoid that operates to move the valve to one of atleast two positions. In one position, the valve 210 may providepressurized gas to output port A and vent pressurized gas from outputport B (i.e., the “closed” position). In this position, pressurized gascan pass through output valve 210 to output port A where the pressurizedgas provides pneumatic power to tool 103. Pressurized gas may also passthrough output valve 210 and muffler 225 where it is exhausted to theatmosphere. In another position (i.e., the “open” position), outputvalve 210 allows pressurized gas to pass to output port B through valve265 where the pressurized gas provides pneumatic power to tool 103.Pressurized gas may also pass through output valve 210 to muffler 225where it is exhausted to the atmosphere. Output valve 210 may also becontrolled by controller 300. In some embodiments, the controller 300may signal the solenoid valve to close during the closed position (asolenoid may act to move the valve to divert air through port A) and,upon discontinuing the signal (or sending an open signal), a spring (orother actuating mechanism) may return the valve to the open position (inwhich the valve is in a position to divert air to port B). During avalve duty cycle of 50%, the controller may apply the close signal forapproximately the same amount of time that the signal is discontinued(the open position) or an open signal is applied.

In some embodiments, manifold assembly 235 may be machined out of ametal, such as aluminum, or plastic. Other materials are alsocontemplated. Manifold assembly 235 may be air tight, contain variousfittings and couplings, and may be designed to withstand relatively highgas pressures. Manifold assembly 235 may be manufactured as a collectionof individual pieces or may be manufactured as a single piece. Forexample, manifold assembly 235 may be machined from a single piece ofaluminum. Mufflers 225, 230, 251, and 253 may suppress noise made byescaping gas.

FIG. 3 illustrates a schematic of a controller 300 and valves 205, 210,261, 263, and 265 for a pneumatically powered vitrectomy machine,according to an embodiment. In some embodiments, controller 300 may sendcontrol signals to valves 205, 210, 261, 263, and 265 via interfacescoupling the valves to the controller. Interfaces may include electricalconductors such as wires, buses, traces, etc. Controller 300 may be anintegrated circuit capable of performing logic functions. Controller 300may include an integrated circuit package with power, input, and outputpins. In various embodiments, controller 300 may be a valve controlleror a targeted device controller. In such a case, controller 300 mayperform specific control functions targeted to a specific device, suchas a valve. In some embodiments, controller 300 may be a microprocessor.Controller 300 may be programmable so that it can function to controlvalves as well as other components of the machine. In some embodiments,controller 300 may be a special purpose controller configured to controldifferent valves that perform different functions.

FIG. 4 illustrates an embodiment of a tool 103 (such as a vitrector)that may be attached to output ports A and B to act as a cutting device.The cutter 403 may be moved by a cylinder that in turn is moved bypressurized gas. The cylinder may oscillate as pressurized gas isalternately directed to output ports A and B. Such a vitrectomy devicemay be designed to operate at various cut rates (e.g., 1000 cuts perminute, 2500 cuts per minute, 5,000 cuts per minute, etc). Other cutrates are also contemplated. Port A and Port B may provide separatepneumatic channels (and a differential pressure between the twochannels) for driving a tool 103. Alternating pressure pulses may begenerated by a four way solenoid valve (e.g., vitrectomy cutter controlvalve 210) cycling pressure output between the two channels. As seen inFIG. 4, the pressure differential may move a diaphragm 401 reciprocallyinside the tool 103 (e.g., a probe) to move the linked probe cutter 403on tool 103. A pressure bias in the two pneumatic channels (e.g.,resulting in a higher pressure differential in either the open or closeposition of the valve) may affect the function and/or performance of thetool 103. Because of various factors (e.g., valve to valve variationsand flow restriction/resistance variations in the two channels fromconsole to console), pressure differentials may vary between differentvalves 210 in different consoles 101 resulting in difficulty providing aconsistent operating pressure differential. To control the pressuredifferentials of the two pneumatic channel output, software may be usedto control the solenoid valve 210 open/closed timing (also known as thevalve duty cycle). The valve duty cycle may be adjusted throughcalibration to better balance the differential pressure during both theopen/closed positions of the valve. By adjusting the valve duty cycle,the time for delivering pressurized air to each pneumatic channel in avalve open/closed cycle may be lengthened or shortened to achieve a moreconsistent differential pressure throughout the valve cycle for smoothertool operation.

For example, at 2500 cuts per minute probe rate, valve 210 may providepressurized air alternately to port A and port B at a rate ofapproximately 24 ms per cycle. To obtain a cut rate of 2500 cuts perminute, the two pneumatic channels may cycle on/off every 24 ms (2500cuts/min or 1 min/2500 cuts*60 seconds/1 min=0.024 seconds/cut=24ms/cut), which may open for 12 ms to each channel. In some embodiments,a transition time to actually open and close the channels may use partof the cycle time. For example, pneumatic channel 1 (i.e., via port A ofcontrol valve 210) may take 4 ms to open (while pneumatic channel 2 isclosing) and 2 ms to close (while pneumatic channel 2 is opening) for atotal transition time per 24 ms cycle of 6 ms. Other transition timesare also contemplated. Because of the transition time, the valve mayactually be open only 8 ms (12 ms−4 ms) to channel 1 while closed tochannel 2 and may be closed for 10 ms (12 ms−2 ms) to channel 1 whileopen to channel 2. This valve timing difference of 8 ms vs. 10 ms inproviding pressurized air to channel 1 and channel 2 can result in anunbalanced pressure differential in the two channels. In someembodiments, it may be desirable for the open time durations of the twochannels to be approximately the same (e.g., in the case of 2500cuts/minute, actually open for approximately (24 ms−6 ms)/2=9 ms). Ifthe transition timings are constant for all valves 210 then softwarecontrol may adjust the valve duty cycle to achieve approximately equalactual open time durations for both channels. In this example, softwaremay adjust the nominal open time to 13 ms for channel 1 and 11 ms forchannel 2. Thus, for this example, excluding transition time, the actualopen time of channel 1 may be 13 ms−4 ms=9 ms and the actual open timeof channel 2 may be 11 ms−2 ms=9 ms (similar to channel 1). However,because the transition time may vary between various valves 210 (e.g.,due to manufacturing variances in the valve 210), a fixed timing offsetmay not successfully counter the imbalance. For example, a differentvalve may take 3 ms (instead of 4 ms) to open channel 1 (while pneumaticchannel 2 is closing) and 2 ms to close channel 1 (while pneumaticchannel 2 is opening). Applying the same software control valve dutycycle (e.g., 13 ms nominal open time for channel 1 and 11 ms nominalopen time for channel 2), the actual open time for pneumatic channel 1may be 13 ms−3 ms=10 ms and the actual open time for channel 2 may be 11ms−2 ms=9 ms. Therefore, in this example, pneumatic channel 1 may remainactually open 1 ms or 11% longer than pneumatic channel 2. Thedifference may result in an uneven power balance between the twopneumatic channels which may result in a lower effective cuttingrate/power. Similarly a fixed timing offset may not successfully counterthe imbalance caused by the flow restriction/resistance variations inthe two channels from console to console.

In some embodiments, a valve duty cycle may be adjusted for individualvalves and or console bases (e.g., to compensate for the differenttransition times of various valves and flow restriction/resistancevariations of various consoles). By applying an adjusted valve dutycycle to the cycle times for the pneumatic channels, the pneumaticchannels may be actuated during the total cycle time to haveapproximately equal actual open times. As noted above, a 50% valve dutycycle may correspond to applying a signal to close the valve forapproximately the same amount of time as the signal is not applied(corresponding to the open position). An adjustment of 1% may result ina 51% valve duty cycle that corresponds to applying a signal to closethe valve for approximately 51% of the total cycle time (and 49% of thetotal time no signal (or an open signal) is applied to open the valve).The longer 51% valve duty cycle may thus compensate, for example, for avalve that takes longer to close than it does to open and or a consolethat has higher flow restriction/resistance in the channel connecting toclose position of the valve.

In some embodiments, a valve duty cycle value for the valve 210 may bestored in a memory 303 on the console 101 or tool 103. The memory 303may include a DIP switch (a dual in-line package switch), a variableresistor, digital potentiometer, or an EEPROM (electrically erasableprogrammable read-only memory). In some embodiments, the valve dutycycle may be determined through trial and error and may be programmed orwritten into the memory 303 (e.g., at manufacture) or may be received,for example, through user interaction with the console 101 (e.g., as avalue entered into a graphical user interface 107 of the console 101).The valve duty cycle may then be used by the surgical console 101 (e.g.,controller 300 in surgical console 101) to control the open/close timesof the valve 210.

As seen in FIG. 5 a-6, one or more DIP switches S1, S2, S3, etc. may beconnected to a network of resistors (each of which may have a differentresistance). FIGS. 5 a and 5 c illustrate embodiments with 5 DIPswitches and FIGS. 5 b and 6 illustrate embodiments with 6 DIP switches.FIG. 5 d illustrates an embodiment with n DIP switches. Each DIP switchmay be programmed with a 1 or 0 (switch on or off) to allow currentthrough its corresponding resistor or to block current from itscorresponding resistor. The network of resistors and DIP switches mayhave a total resistance that is based on the DIP switch settings. Forexample, with 6 DIP switches (each with a corresponding resistor), thenetwork of resistors may be configured to have a resistance selectedfrom 2̂6=64 possible resistances. Combinations of the DIP switch settingsmay therefore produce different resistant values of the resistornetwork. For example, above each resistor in FIGS. 5 a-6 are exampleresistance multiples (e.g., in kilohms) (other resistances are alsopossible). As seen in FIG. 5 a, example network resistances may be 1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 basedon the settings of the 5 DIP switches (in the configuration shown, 32DIP switch combinations may produce 20 network resistance values inincrements of 1 along with 12 duplicates). Other configurations are alsopossible (e.g., different resistance values, different DIP switchplacements, etc). In the embodiment shown in FIG. 5 b, 64 DIP switchcombinations may produce 40 network resistance values in increments of0.5 along with 24 duplicates (e.g., network resistance values or 1, 1.5,2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10,10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17,17.5, 18, 18.5, 19, 19.5, 20, and 20.5). As seen in FIG. 5 c, 5 DIPswitch resistor network may include 32 DIP switch combinations toproduce 32 network resistance values in increments of 1 withoutduplicates (e.g., resistance values of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,29, 30, 31, and 32). As seen in FIG. 5 d, an n DIP switch resistornetwork may include 2^(n) DIP switch combinations to produce 2^(n)network resistance values in increment of R without duplicates (e.g.,resistance values are R, 2R, 3R, 4R, 5R, . . . , 2^(n)R). A knownvoltage (e.g., 5 volts) may be applied to the resister network (e.g., byvoltage source 501) and a resulting voltage may be converted to adigital count 511 by an analog/digital converter 509. Software executingon the surgical console may use the digital count 511 to determine acorresponding valve duty cycle. For example, a table lookup may beperformed on the digital count to determine a corresponding valve dutycycle value. In some embodiments, a calibration table 901 (e.g., seeFIG. 9) may be stored on the console with digital counts andcorresponding valve duty cycle values.

As noted above, the DIP switches (e.g., in the set of DIP switches 503)may be programmed in various on/off (I/O) positions to combine selectedresistances in the network of resistors 505. The network of resistorsmay act as a voltage splitter to output a second voltage as a result ofthe first voltage applied to the network. The ADC 509 may convert thesecond voltage into a digital count 511. For example, Voltage 2 mayresult in a digital count of 447 (e.g., corresponding to a voltage of2.183 Volts). Software executing on the surgical console may use thedigital count of 447 to determine a corresponding valve duty cycle (inthis case 49.5%). For example, as seen in FIG. 9, a look-up table may beaccessed to determine a valve duty cycle corresponding to the digitalcount. In some embodiments, the valve duty cycle may be determined andstored in a writable memory (e.g., an EEPROM). During subsequent uses ofthe surgical consoles, the EEPROM may be read instead of determining thevalve duty cycle through use of the DIP switches. Using the EEPROM forsubsequent uses may allow for a quicker determination of the valve dutycycle. Using the EEPROM may also prevent false values associated withthe DIP switches being inadvertently switched or bumped or set byunauthorized personnel. In some embodiments, a new valve duty cycle maybe read into the EEPROM when the surgical console receives an indicationthat a new value is being determined (e.g., a user may enter a passwordin the user interface to authenticate the user and set the console forreceiving a new valve duty cycle or a user may set a switch or press abutton near the DIP switches indicating to the surgical console todetect and store a new valve duty cycle in the EEPROM (e.g., asdetermined from the DIP switches).

FIG. 7 illustrates a method for determining a valve duty cycle forcalibrating valve 210. The elements provided in the flowchart areillustrative only. Various provided elements may be omitted, additionalelements may be added, and/or various elements may be performed in adifferent order than provided below.

At 701, pneumatic ports of a valve 210 to be calibrated may be coupledto one or more pressure sensors for determining the pressure of eachport (or a differential pressure between the ports) during operation ofthe valve 210. For example, separate pressure sensors may be coupled toeach port (A and B) or a differential pressure sensor may be coupled toboth ports A and B. If using separate pressure sensors on each port, adifferential pressure may be calculated using the pressure data fromeach port. As seen in FIG. 1, tool 103 may be a pressure transducer boxwith the one or more pressure sensors coupling to the A and/or B portsthrough ports 105. In some embodiments, the valve 210 may be testedwhile coupled to the surgical console (e.g., the pressure sensors may becoupled to the output pneumatic ports 105 of the surgical console 101).In some embodiments, a cuts per minute setting may be set for the valve(e.g., 2500 cuts per minute).

At 703, the pneumatic system valve duty cycle may be set to a defaultvalue (e.g., the calibration DIP switches may be set to 50% valve dutycycle which may result in no applied offset to the open/close valvetiming). The DIP switch settings may be set using a calibration table901 that relates DIP switch settings to valve duty cycles.

At 705, pneumatic system (including valve 210) may be operated for agiven amount of time (e.g., 10 seconds). During the pneumatic systemoperation, pressure data for the run may be detected through thepressure sensors. In some embodiments, a footswitch treadle may bedepressed to activate the pneumatic system. In some embodiments, thepneumatic system may be operated for an extended time (e.g., 1 to 2hours) especially if the pneumatic system and/or console is new. Theextended operation prior to calibration may allow the system and/orconsole to settle out initial valve variations due to manufacturing,friction points, and other component interaction points (e.g., initialfriction on new parts may be worn down as the new part interacts withother parts for the extended period). In some embodiments, the pneumaticsystem may be discontinued after the initial run and then operated againfor another set amount of time (e.g., 5 to 10 seconds) before taking thepressure data. In some embodiments, a wait time (e.g., 5 to 10 seconds)may be applied between pneumatic system runs.

At 707, pressure differentials and pressure range between the open/closevalve positions may be determined. FIG. 8 a illustrates a plot of apossible pressure differential versus time for a pneumatic system. Asseen in FIG. 8 a, at cycle interval time (T), the pressure differentialsmay be +10 and −13 psi (pounds per square inch) on the open/closepositions (resulting in a pressure range 801 of approximately 23 psi).The lowest performance point may be the cycle interval time when thedifferential pressure difference between the pressure open and pressureclosed is the lowest (i.e., when (abs(pressure open)+abs(pressureclosed)) is at a minimum for the pressure data. In the case shown inFIG. 8 a, there is a noticeable dip in pressures for the open and closedposition at cycle interval time (T).

At 709, a valve duty cycle to compensate for the pressure bias may bedetermined. In the pressure data shown in FIG. 8 a, at cycle intervaltime (T), the pressure bias appears to be approximately 3 psi(associated with the −13 psi reading over the +10 psi reading). A valveduty cycle that would result in approximately centering the pressuredifferential (e.g., aimed at obtaining open/close pressure values ofapproximately +11.5 psi and −11.5 psi at cycle interval time (T)) may bedetermined. Determining the valve duty cycle to center the pressuredifferentials at the lowest performance point of the pneumatic systemmay insure that the pneumatic system has sufficient pressure to operatein both the open and closed positions at its lowest performance point(the valve duty cycle may also result in improved performance at theother operating points of the pneumatic system). While several examplesherein determine a valve duty cycle around the lowest performance point,a valve duty cycle may also be determined using other points in thepressure data. Determining a valve duty cycle may be calculated asfollows:

New valve duty cycle=Previous valve duty cycle+(((abs(openpressure)−abs(closed pressure))/2)*(valve duty cycle delta/differentialpressure change delta))

Where open pressure and closed pressure are taken at a time of lowestperformance for the pneumatic system (e.g., time T in the currentexample) and where abs( ) represents the absolute valve. In someembodiments, the valve duty cycle to pressure differential adjustmentratio may be determined mathematically or through trial and error. Forexample, the ratio may be 1% (valve duty cycle delta) to 0.86 psi(differential pressure change delta).In the current example:

New valve duty cycle=50%+(((13 psi−10 psi)/2)*(1%/0.86 psi))

New valve duty cycle=50%+(1.5 psi*(1%/0.86 psi))

New valve duty cycle=50%+1.744%=51.744%

Thus, the pressure on the close side (currently+10 psi) may be increasedto 11.5 psi with the new valve duty cycle of 51.744% (10psi+1.744%*(0.86 psi/1%)=11.5 psi) and the open side may be shifted to−11.5 psi (−13 psi+1.744%*(0.86 psi/1%)=−11.5 psi). In some embodiments,the valve duty cycle may be rounded to a nearest increment (e.g.,rounded to 51.5% if rounding to nearest increments of 0.5%).

At 711, the pneumatic system may be programmed with the new valve dutycycle. For example, the DIP switches (which may be physically accessibleswitches with on/off or I/O options) may be set in an on/off sequencethat will produce a voltage corresponding to the determined valve dutycycle. In some embodiments, the new valve duty cycle may be computed bythe surgical console and/or entered into a graphical user interface ofthe surgical console.

At 713, the pneumatic system may be operated again (e.g., 5 to 10seconds). During the pneumatic system operation, pressure data for therun may be detected through the pressure sensors. In some embodiments,the pneumatic system may be discontinued after the initial run and thenrun again for another set amount of time (e.g., 5 to 10 seconds) beforetaking the pressure data. In some embodiments, a wait time (e.g., 5 to10 seconds) may be applied between pneumatic system runs.

At 715, pressure differentials and pressure range between the open/closevalve positions may be determined again. FIG. 8 b illustrates a possibleplot of pressure data after applying the new valve duty cycle. As seenin FIG. 8 b, the pressure differential may now be approximately centeredaround 0 psi such that the pressure differential in the closed positionis approximately 11.5 psi at the lowest performance point for the closedposition and approximately −11.5 psi for the lowest performance point inthe open position.

At 717, pressure differentials, pressure range, and/or pressure bias maybe compared to acceptable limits. In some embodiments, the pressuredifferentials (e.g., in the corrected case the differentials areapproximately +11.5 psi and −11.5 psi as seen in FIG. 8 b), may becompared to a predetermined threshold for operation (e.g., the absolutevalues of the differentials may be compared to a threshold ofapproximately 10 psi). In the corrected case shown in FIG. 8 b, thedifferential pressures (absolute values for comparison purposes) aregreater than the threshold of 10 psi. In some embodiments, a pressurebias (the pressure difference between the two channels) may also bedetermined and compared to a predetermined acceptable limit. Forexample, the pressure bias may equal to abs(closed pressure)−abs(openpressure). After calibration, a predetermined acceptable pressure biaslimit of 1 psi may be used (other pressure bias may also be useddepending on the pneumatic system calibration). As another example, thetotal pressure range (abs(open pressure)+abs(closed pressure)) may becompared to a predetermined acceptable limit (e.g., a minimum 21.6 psiof range). In some embodiments, the total pressure range at a point oflowest performance for the pneumatic system may be compared to anacceptable total pressure range to determine if the pneumatic system hasa leak or restriction. For example, if the total pressure range is <21.6psi, there may be a leakage or restriction in the system. Other totalpressure range may also be used (different pneumatic systemconfigurations may operate at different pressures and pressure ranges).If the total pressure range at the lowest performance point does notmeet the minimum acceptable limit, the valve may be replaced and/or thepneumatic system may be checked. Also, if edges of pressure wave formare not smooth, but are wavy or have shifts, or are not expanding onboth sides after the minimum performance points, the valve may need tobe replaced.

At 719, if the total pressure range or pressure bias is out of theacceptable range, a new valve duty cycle may be used. In someembodiments, the new valve duty cycle may be recalculated. For example:

New valve duty cycle=Previous valve duty cycle+(((abs(openpressure)−abs(closed pressure))/2)*(valve duty cycle delta/pressurechange delta))

Where open pressure and closed pressure may be differential pressures ata time of lowest performance for the pneumatic system. In someembodiments, instead of using the equation, a valve duty cycle that isone increment above or below the previous valve duty cycle may be tried.If the previous closed pressure needs to be increased (to reduce thepressure bias toward the open position), the valve duty cycle may beincreased to the next increment (e.g., from 51% to 51.5%) or vice versa.In some embodiments, the new valve duty cycle may be determined by thesurgical console and/or entered into a graphical user interface of thesurgical console. In some embodiments, DIP switches may be set tocorrespond to the new determined valve duty cycle. The new valve dutycycle may then be tested (e.g., by performing elements 713 to 719)

At 721, if the valve has been tested more than a set number of times(e.g., twice) and the total pressure range or pressure bias is still outof the acceptable range, a different valve/module may be installed. Insome embodiments, additional rounds of determining a new valve dutycycle (or the DIP switches may be moved to correspond to another valveduty cycle above or below the previous one) may be performed.

At 723, if the total pressure range and the pressure bias from 717 arewithin the acceptable ranges, the calibration process may be concluded.The surgical console may use the determined valve duty cycle. In someembodiments, the DIP switches and resistance network may relay thedesired valve duty cycle (through a characteristic voltage) to thesystem console during operation. For example, a voltage from theresister network may be converted into a digital count through ananalog/digital converter 509. The digital count may be processed bysoftware executing on the surgical console and a corresponding valveduty cycle may be determined and used to modify the valve performance.In some embodiments, the calibration process may be performed multipletimes to insure repeatability of the calibration results with thedetermined valve duty cycle.

In some embodiments, the vitrectomy system may include one or moreprocessors (e.g., controller 300). The controller 300 may include singleprocessing devices or a plurality of processing devices. Such aprocessing device may be a microprocessor, controller (which may be amicro-controller), digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, control circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on operational instructions. Memorycoupled to and/or embedded in the processors may be a single memorydevice or a plurality of memory devices. Such a memory device may be aread-only memory, random access memory, volatile memory, non-volatilememory, static memory, dynamic memory, flash memory, cache memory,and/or any device that stores digital information. Note that when theprocessors implement one or more of its functions via a state machine,analog circuitry, digital circuitry, and/or logic circuitry, the memorystoring the corresponding operational instructions may be embeddedwithin, or external to, the circuitry comprising the state machine,analog circuitry, digital circuitry, and/or logic circuitry. The memorymay store, and the processor may execute, operational instructionscorresponding to at least some of the elements illustrated and describedin association with, for example, FIG. 7.

Various modifications may be made to the presented embodiments by aperson of ordinary skill in the art. It is intended that the presentspecification and examples be considered as exemplary only with a truescope and spirit of the invention being indicated by the followingclaims and equivalents thereof.

What is claimed is:
 1. A surgical console, comprising: a valve; at leasta first port and a second port coupled to the valve, wherein the valveis configured to provide pressurized gas alternately to each of thefirst port and the second port to drive a pneumatic tool coupled to thesurgical console; a controller coupled to the valve, wherein thecontroller is operable to control the valve open and close times,wherein a valve open time corresponds to a time to open a first port andwherein a valve close time corresponds to a time for closing the firstport, wherein closing the first port coincides with opening a secondport such that pressurized air is being directed by the valve eitherthrough the first port or the second port; wherein the controller isconfigured to adjust the valve open/close times according to a valveduty cycle; wherein the valve duty cycle corresponds to an adjustmentdetermined by analyzing operating pressure data for the open and closedvalve positions and determining the adjustment for at least one of thevalve open time and valve close time that will result in open and closedoperating differential pressures above a predetermined threshold.
 2. Thesurgical console of claim 1, wherein the valve is a four-way solenoidvalve.
 3. The surgical console of claim 1, further comprising apneumatic tool coupled to the surgical console, wherein the pneumatictool is a vitrectomy cutter.
 4. The surgical console of claim 1, whereinthe valve duty cycle is stored on a memory accessible by the controller.5. The surgical console of claim 1, wherein a total valve time equalsapproximately the valve open time plus the valve close time for a valvecycle, and wherein the valve duty cycle is a percentage of the totalvalve time for the controller to signal the valve to direct gas throughthe first port.
 6. The surgical console of claim 1, wherein the newvalve duty cycle is determined using pressure data during testing of thesurgical console, wherein the new valve duty cycle is approximatelyequal to a previous valve duty cycle+(((abs(open pressure)−abs(closedpressure))/2)*(valve duty cycle delta/differential pressure changedelta)) where the previous valve duty cycle is the valve duty cycleduring testing, open pressure and closed pressure are differentialpressures for the port for one cycle of the valve, and wherein the valveduty cycle delta/differential pressure change delta is a ratio of valveduty cycle change to resulting differential pressure change.
 7. Thesurgical console of claim 6, wherein the open pressure and closedpressure for the port are taken during a lowest performance point forthe pneumatic system.
 8. The surgical console of claim 7, wherein thelowest performance point is the point when the absolute differentialpressure difference between the open pressure and closed pressure is thelowest such that (abs(pressure open)+abs(pressure closed)) is at aminimum for the measured pressure data.
 9. The surgical console of claim1, further comprising a plurality of DIP switches and a plurality ofresistors, wherein the DIP switches are configurable to combine one ormore of the plurality of resistors in a resistor network such that uponapplying an input voltage to the resistor network, an output voltage ofthe resistor network is indicative of a valve duty cycle.
 10. Thesurgical console of claim 9, further comprising an analog to digitalconverter to convert the output voltage to a digital value, whereinsoftware executing on the surgical console is operable to determine avalve duty cycle that corresponds to the digital count through a look-uptable.
 11. A method of calibrating a surgical pneumatic system,comprising: operating a pneumatic system comprising a pneumatic valveconfigured to cycle between an open position and a closed positionwherein pressurized gas is directed at a first port when the valve is inthe open position and wherein pressurized gas is directed at a secondport when the valve is in the closed position; measuring pressuresoutput by the pneumatic valve, wherein the measured pressure datacomprises an open differential pressure corresponding to a differentialpressure between the first port and the second port during the openposition and a closed differential pressure corresponding to adifferential pressure between the first port and the second port duringthe closed position; and calculating a new valve duty cycle, wherein thenew valve duty cycle is approximately equal to a previous valve dutycycle+(((abs(open pressure)−abs(closed pressure))/2)*(valve duty cycledelta/pressure differential change delta)) where the previous valve dutycycle is the valve duty cycle during operation of the pneumatic systemwhile measuring the pressures, open pressure and closed pressure are themeasured differential pressures for the port during a corresponding openposition and closed position of one cycle of the valve, and wherein thevalve duty cycle delta/pressure differential change delta is a ratio ofvalve duty cycle change to resulting differential pressure change. 12.The method of claim 11, wherein the open pressure and closed pressurefor the port are taken during a lowest performance point during themeasured pressures for the pneumatic system.
 13. The method of claim 11,further comprising using the new valve duty cycle to modify the valveopen position timing.
 14. The method of claim 3 further comprising:operating the pneumatic system and measuring pressures output by thepneumatic valve; calculating a total pressure range, wherein the totalpressure range is approximately equal to the sum of absolute values ofthe open pressure and the closed pressure; and determining if the totalpressure range is greater than a predetermined total pressure rangelimit.
 15. The method of claim 13, further comprising: operating thepneumatic system and measuring pressures output by the pneumatic valve;calculating a pressure bias, wherein the pressure bias is approximatelyequal to abs(closed pressure)−abs(open pressure); determining if thepressure bias is less than a predetermined pressure bias limit.
 16. Themethod of claim 15, wherein the open pressure and the closed pressureare the differential pressures during a lowest performance point duringpressure measuring.
 17. The method of claim 16, wherein the lowestperformance point is the point when the pressure difference between theopen pressure and closed pressure is the lowest such that (abs(pressureopen)+abs(pressure closed)) is at a minimum for the measured pressuredata.